Telephone-exchange system



TELEPHGNE EXCHANGE SYSTEM Filed March 1920 2 Sheets-Sheet 1' ,sists' inthe provision Patented Apr. 2.2, 1924.

tFNETE STATES PATET QFFIQE.

any L. STOKELY, or :cLonxi. PARK, new

' Maui? YORK, ASSIGNOR TO W'TESTEBN ELECTRIC CDMIANY, INCORFORATED, OFNEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filcd'march 4,

T aZZ whom it may concern Be it known that I, RAY L. S'roxnL'Y, a.citizen of the United States, residing at Floral Park, in the county ofNassau, State of New York, have invented certain'new and usefulImprovements in Telephone- Exchange Systems, of which the following is afull, clear, concise, and exact description.

This invention relates to telephone exchange systems and moreparticularly to such systems involving two central otlices or twoprivate branch exchanges. More specifically, the invention relates to asysterm in which there is one central office in which both manual andautomatic switching apparatus is employed in interconnecting subscriberslines, and another ofiice in which an operator manually completes theconnections. Extending betweenthe otlices are trunk lines over which asubscriber at an automatic substation may call the operator at themanual exchange or, the operator at the manual exchange may call asubscriber at an automatic substation or an operator at the automaticexchange. The operator at the first-mentioned exchange has access to thetrunk lines extending between the otfices.

An object of the invention is to provide improved signaling means insystems of this nature. I

A further object of the. invention is to provide means for efficientlysupervising and handling the tratlic in such a system with a minimum ofapparatus.

A feature of the invention consists in utilizing a. slow-to-releaserelay of a selector switch employed in settingthe switch tor controllingthe application of ringing current to the trunk circuit to operate a signaling device associated therewith.

A further feature of the invention c0nof means for en abling' anoperator at change to listen in todetermine the inn portance ofconversations over the trunk circuits and for extending connections overthe trunk circuit to the operator at the manual exchange when the trunkcircuit is idle. 1

his thought that the invention will be best understood from thefollowing detailed description, reference being had to the accompanyingdrawings.

in the drawings, Fig. 1 shows the subthe automatic ex-' 1920. 7 SerialNo. 363,275.

station of an automatic subscriber A whose line terminates in anon-numerical switch, schematically represented as B. Accessible to thenon-numerical switch is a selector switch such as (land connector switch(not shown) over which automatic inter-connections may be had with otherautomatic stations. Accessible to the selector (3, is a trunk circuitextending from the first or automatic exchange to a secondor manualexchange. E shows a portion of a cord circuit by means of which anoperator at the first exchange may listen in on the trunk or completeconnections over the trunk lead ing to the second exchange. D representsschematically a. non-numerical switch by means of which the operator atthe manual exchange may establish a connection with an automaticsubscriber or the operator at the first exchange. Fig. 2 shows that portion of the trunk'circuit at the second exchange. A portion of aconnecting cord H is shown by means of which an operator may completecalls to a line terminating at er position (not shown) and a dialingcord 1*: by means of which automatic switches at the first exchange maybe controlledover the trunk circuit. For the sake of clearness only onesubscribers line selector switch, one trunk and one of each of the cordcircuits are shown, it being understood that there may be a plurality ofsubscriber lines such as A, terminating in non-numerical switches at thefirst exchange, a plurality of selector switches such as C and aplurality of trunk circuits. There may also be a plurality of cordcircuits such as E at the first exchange.

Manual subscribers lines and trunk lines ifrcm other exchanges mayterminate at the operators position at the first exchange in jacksin-the well-known manner. Such line and trunk circiiiits are wol knownandto avoid complicating the drawing they have Been omitted therefrom.At the second exchange there may be a plurality of cord circuits such asH with a single dialing cord K for each position. Subscribers? lines(not shown) of the wellslrnown type may terminate in jacks atthe'operato'fis position at the second exchange.

The system will be best understood from a description of the operationthereof.

It the subscriber whose substation is indicated at A desires aconnection with an operator at the manual exchange, he will remove thereceiver from the switchhook, whereupon his line will be extended to thefirst selector C in any well-known manner, it being assumed in thepresent case that a non-numerical switch, schematically indicated as B,is utilized for this purpose.

As soon as the calling line is extended tothe first selector C, linerelay 3 is energized over a circuit extending from grounded battery,lefthand winding of relay 3, back contact and outer left-hand armatureof relay 9, terminal 4, brush 5, the loop of the calling subscribersline, brush 7, terminal 6, inner left-hand armature and back contact ofrelay 9, and righthand winding of relay 3 to ground. The resultantenergization of relay 3 completes a circuit from grounded batterythrough the winding of slow-to-release relay 8, front contact andarmature of relay 3 and outer right-hand armature and back contact ofrelay 9 to ground. When the subscriber operates his impulse sender S totransmit the first series of impulses, line relay 3 will beintermittently deenergized in response to such impulses. Upon the firstdeenergization of line relay 3, a circuit is closed from groundedbattery, through the winding oi primary magnet 10, winding ofslow-torelease relay 11, front contact and righthand armature of relay8, back contact and armature of relay 3 and back contact and outerright-hand armature of relay 9 to ground. Relay 3 being of the slow-torelease type retains its armatures attracted during the sending ofimpulses. Relay 11 and magnet 10 are energized in this circuit and thelatter causes the brushes of the first selector to be moved in a primaryor group selecting direction. The energization of relay 11, completes acircuit from ground, left-hand armature and front contact of relay 8,alternate contacts of relay 11, oifnormal contacts 12, which are closedin response to the sending of the first impulse, and Winding of relay 13to grounded battery to actuate relay 13 upon the movement of the brushshaft from normal. Slow-'to-release relay 11 retains its armaturesattracted during the sending of the first series of impulses in responseto which the stepping magnet 10 is intermittently energized to advancethe brushes into operative relation with the group of trunks leading tothe manual exchange through which a desired line may be reached.

Upon completion of the first series of impulses, line relay 3 remainsenergized for a comparatively long interval, and relay 11 and primarymagnet 10 are deenergized. WVhen relay 11 deenergizes, relay 13 is heldup over a path including grounded battery, Winding of relay 13,oil-normal contacts 12, normal contacts of magnet 14. front contact andleft-hand armature of relay 13, outer right-hand armature and contact ofrelay 9 to ground. Relay 11 in retracting its armatures completes acircuit for secondary magnet 14 over a path extending from groundedbattery, winding of magnet 14, right-hand armature and front contact ofrelay 13, normal contacts of relay 11, and front contact and lefthandarmature of relay 8 to ground. Magnet 14 in operating steps the brushesone step into engagement with the first terminal in the selected groupof trunk terminals, and opens the locking circuit for relay 13 causingits deenergization. Magnet 1& thereupon deenergizes. Should the firsttrunk be busy, ground will be present on the test terminal 20 thereof,which will maintain the shunt around relay 9 and prevent it fromenergizing. Relay 13 will then be energized over a circuit extendingfrom ground on terminal 20, brush 17, in ner right-hand armature andback contact of relay 9, back contact and armature of magnet 1 1,off-normal contacts 12, and winding of relay 13 to grounded battery.Relay 13 upon actuation again completes a circuit for magnet 1 1 whichmoves the brushes another step, whereupon relay 13 and magnet'14c againdeenergize. As soon as the test brush 17 encounters an idle trunk havinga contact corresponding to 20, upon which there is no ground, a circuitis completed extending from ground, left-hand armature and front contactof relay 8, winding of relay 9, back contact and armature of magnet 14:,off-normal contacts 12, and winding of relay 13 to grounded battery.Relay 9 then operates but relay 13 being marginal, will not operate dueto the high resistance of relay 9, and the selector ceases stepping.

Relay 9 in operating disconnects relay 3 from the line and completescircuits for relays 29, 26, and 3+1 of the trunk circuit. Relay 29 inenergizing completes circuits for relays and the latter controls thereversing of the current flow over the trunk circuit and the former, theactuation of relays 25 and 24:. The circuit for relay 29 extends fromground, left-hand winding of coil 21., upper left-hand winding ofrepeating coil 22, terminal 18, brush 15, front contact and innerleft-hand armature of relay 9, tern'iinal 6, brush 7, through thesubstation loop, brush 5, terminal at, outer lefthand armature and frontcontact of relay 9, brush 16, terminal 19, lower left-hand Winding ofrepeating coil 22, right-hand winding of coil 21, and winding of relay29 to grounded battery. Relay 29 upon actuation completes a circuit atits right-hand armature and front contact for slow-to-release relay 23and at its left-hand. armature and front contact for relay Relay 23 inoperating places ground on the test terminal 20 through the right-handWinding of relay 24 to maintain the selected trunk busy and causes relay25 to operate thereby rendering the trunk circuit continuous anddisconnecting the non-nuinerical switch D from the trunk. The circuitscompleted by relay 23 may be traced as follows: ground, righthandarmature and front contact of relay 23, and thence in parallel, one pathextending through the winding of relay 25 to grounded battery and theother through the right-hand winding of relay 24, front con tact andleft-hand armature of relay 23 to terminal 20. The instant relay 9attracted its armatures, a circuit for relay 26 was completed therebymomentarily connecting ringing current from a source to the trunk andprojecting said ringing current over the trunk to the manual exchange toactuate a relay 107 thereat as soon as relay 25 operated. The circuitfor relay 26 is automatically interrupted as soon as slow to-releaserelay 8 releases its armatures and relay 24 energizes. Relay 2 1energizes over the path previously traced and in attracting itsright-hand armature short-circuits its right-hand Winding therebyplacing a direct ground on the conductor leading to terminal 20. Alocking circuit is completed through the left-hand Winding of relay 2&to maintain said relay 24 energized. Relay 26 thereupon deenergizes.Ground at" the righthand armature of relay 23 is substituted for theground at relay 8 to hold the trunk and selector busy. The circuit forthe energization of relays 26 and 34 may be traced as follows: ground,left-hand armature and front contact of relay 8, front contact and innerrighthand armature of relay 9, brush 17, terminal 20, and thence inparallel one path extending through the back contact and lefthandarmature of relay 2 1, inner left-hand armature and back contact ofrelay 27 and winding of relay 26 to grounded battery and the otherextending through the outer left-hand armature and back contact of relay27 and the winding of relay 34 to grounded battery. Relay 26 inoperating permits ringing current to flow over the line to the manualexchange to display signal 110 thereat. Relay 34 in operating completesa circuit for busy signal 36 at the operators position thus furnishinga'vi'sual signal to the operator that the trunk is busy and at itsright-hand armatures connectsground and battery through resistances and66 respectively, through'the back contact and righthand armature ofrelay 35 to jack 40 for furnishing a busy test at the jack. The

path for the ringing current may he follows lower source of ringingalternate contacts of traced as current 60,

relay 26, back contact and lower inner armature of relay 30, loweralternate contacts of relay 25, conductor 102, inner normal contacts ofrelay 105, coil 106, winding of relay 107, condenser 108, back contactand left-hand armature of relay 109, outer normal contacts of relay 105,conductor 100, upper alternate contacts of relay 25, upper normalcontacts of relay 30, upper alternate contacts of relay 26 to ground.Relay 107, in operating completes a circuit at its armature and frontcontact for relay 111 which in energizing locks up under control of relay 109 over a circuit including grounded battery, winding of relay 111,left-hand armature and front contact of relay 111, back contact andouter right-hand armature of relay 109 to ground. Relay 111 upon actuation completes a circuit at its right-hand armature and front contactfor signal 110.

The operator observing this signal may insert plug 116 into jack 115,whereupon a circuit is completed for relays 109 and 118, extending fromgrounded battery, winding of relay 118, sleeves of plug 116 and jack 115and left-hand Winding of relay 109to ground. Relay 109 in operatingopens, at its outer right-hand armature and front contact, the lockingcircuit for relay I 111 which retracts its armatures and extinguishesthe signal 110; and at its left-hand armature and front contactestablishes a bridge across the trunk conductors 100 and 102, saidbridge including retardation coil 106, winding of polarized relay 120,front contact and left-hand armature of relay 109. This bridge acrossthe trunk conductors causes relay 31 to operate over a circuit includinggrounded battery, winding of relay 31, left-hand winding of retardationcoil 32, lower right-hand winding of repeating coil 22, lower alternatecontacts of relay 33, upper normal contacts of relays 26 and 30, upperalternate contacts of relay 25, conductor 100, outer normal contacts ofrelay 105, left-hand armature and front contact of relay 109, Winding ofpolarized relay 120,

Winding of'coil 106, inner normal contacts of relay 105, conductor 102,lower alternate contacts of relay 25, lower normalcontacts of relays 30and 26, upper alternate contacts of 'relay 33, upper right-hand windingof repeating coil 22, and right-hand winding of 5 The operator at themanuale-Xchange may then actuate listening key and inquire tors leadingto the manual exchange, thereby releasing polarized relay 120, which, inreleasing its armature, opens the circult for relay 112, and it, inturn, opens the circuit for relay 125, thereby causing the supervisorylamp 126 to light indicating to the operator that the calling subscriberhas disconnected. The operator observing this signal may remove plug 116from jack 115,

- whereupon relay 109 deenergizes and in so doing opens the circuit forrelay 31, which in retracting its armature opens the circuit for relay23. Relay 23 in deenergizing removes ground from test terminal 20,whereupon relay 9 deenergizes thereby completing a circuit for releasemagnet 15 over a path extending from grounded battery, winding of magnet15, off-normal contacts 2, back contact and right-hand armature of relay8, back contact and right-hand armature of relay 3, and back contact andright-hand armature of relay 9 to ground. Magnet 15 in actuatingrestores the selector to normal in the manner well-known. Relay 23 indeenergizing also causes the release of relays 24, 25, 34, and busysignal 36.

If the operator at the automatic exchange desires connection with theoperator at the manual exchange, plug 41 may be inserted into jack 40,whereupon relay 27 is operated over a circuit extending from groundedbattery through lamp 45, resistance 49, sleeves of plug 41 and jack 40,right-hand normal contacts of relay 35, outer right-hand arma ture andback contact of relay 34, and winding of relay 27 to ground. When relay27 operates, circuits are completed for relays 23 andv 30 as follows:ground, armature and back contact of relay 34, right-hand armature ofrelay 27, and thence through the winding of relay 23 and the winding ofrelay 30 in parallel to grounded battery. Relay 23 in operating placesground on the test terminal 20 to render it busy over a circuitextending from ground through the righthand armature and front contactof relay 23, right-hand winding of relay 24, front contact and left-handarmature of relay 23 to terminal 20, and also completes a circuit at itsright-hand armature and front contact for relay 25, which in operatingrenders the trunk circuit continuous and disconnects line finder D fromthe trunk. Relay 30 in operating connects jack 40 to the trunkconductors and completes a circuit for the en ergization of relay asfollows: ground, armature and front contact of relay 23, outer lowerarmature and front contact of relay 30, and winding of relay 35 tobattery. Relays 35 and 25 are held locked up under the control of relay23.

The operator may then actuate the ringing key 43 of the cord circuit E,Whereupon relay 107 is energized and signal 110 is displayed in themanner heretofore described.

When the operator at the manual exchange inserts plug 116 into jack 115in response to the signal 110, supervisory relay 42 and polarized relay120 are operated over a circuit extending from ground, upper right-handwinding of repeating coil 44, upper normal contacts of ringing key 43,tips of plug 41 and jack 40, lower inner alternate contacts of relay 30,lower alternate contacts of relay 25, conductor 102, inner normalcontacts of relay 105. coil 106, winding of polarized relay 120, frontcontact and left-hand armature of relay 109, outer normal contacts ofrelay 105, conductor 100,

I upper alternate contacts of relays 25 and 30,

rings of jack and plug 41, lower normal contacts of key 43, winding ofrelay 42, and

lower right-hand winding of repeating coil- 44 to grounded battery.Relay 42 in oper ating causes a shunt to be placed around supervisorysignal 45 and relay 120 in operating completes a circuit for relay 112,thereby energizing supervisory relay 125 and extinguishing supervisorysignal 126. The operator may then actuate listening key 130, conversewith the calling party and upon inquiring for the number desired,complete the connection in the well-known manner.

Upon completion of conversation and removal of the plug 41 from jack 40,relay 30 at the automatic exchange releases and relay 31 operates. Relay30 in releasing reverses the current through the polarized relay 120,which opens, its contacts, thereby releasing relay 112 and it in turnrelay 1255, thereby lighting the supervisory signal 126. The trunkcircuit is maintained busy until the operator at the manual exchangeremoves plug 116 from jack 115 whereupon relay 109 deenergizes, thusremoving the bridge from the trunk and permitting relay 31 to release.Relay 31 in releasing opens the circuit for relay 23, which deenergizes,thereby removing the ground at its right-hand armature from the testterminal 20, and releasing relays 25 and 35 and restoring all apparatusto normal.

Should the operator at the manual exchange disconnect before theoperator at the automatic exchange disconnects, supervisor lamp 45 atthe automatic exchange wil light. Removal of plug 116 from jack 115before plug 41 is removed from jack 410 will not deenergize relay 112since relay 112 is held up through the contacts of polarized relay 120.Relay 109 will deenergize, how ever, and a high resistance 1 10 isbridged across the line in series with the winding of relay 120. Relay120 remains energized but supervisory relay 4.2 deenergizes due to thehigh resistance of coil 1 10. Lamp 45 then lights indicating t theoperator that the operator at the distant end has disconnected. Plug 11may then be removed from jack 40 whereupon all apparatus is restored tonormal.

In a similar manner relay 31 or" the trunk circuit is deenergized by thebridging of the high resistance 1 10 in the circuit, when, a connectionexists between an automatic subscriber, such as A, and a manualoperator, and the latter disconnects first.

It will be remembered that when a connection exists over the trunkbetween the subscriber at station A and the operator at the manualexchange, busy signal 36 is actuated apprising the operator thereof.Should it be necessary, however, to use the trunk circuit while it isbusy to complete a connection of great importance, the operator maylisten in in the trunk by inserting plug 11 into jack to and, it theexisting connection is not of great importance, inform the parties thatthe trunk is desired. Condensers 16 and 1'? through which jack 40 isnormally connected to the trunk, prevent battery from flowing from thecord circuit E to the trunk circuit. The connection is not disturbed byinserting plug 41 into jack d0 since relay 3% is operated when the trunkis busy. I

The operator at the manual exchange may call a subscriber at theautomatic exchange or the operator at the automatic exchange byinserting the plug 116 of her cord circuit into the jack 115 in whichthe trunk extending to the automatic exchange terminates and operatingthe'impulse sender S Insertion of plug 116 into jack 115011 an outgoingcall from the manual exchange, ope ates the non-numerical switch I) atthe automatic ex change in the well-known manner due to the bridge beingplaced across the trunk conductors 100 and 102. The non-numericalswitchD in operating will connect ground to the test terminal 20 through thebrush 61, thereby rendering the trunk busy to selectors and operaterelay 3%, thereby placing the busy test on jack -40 and operating busysignal 36, as heretofore described. The operator then inserts thedialing" cord 135 into jack 136 and operates the impulse sender to sendout impulses in accordance with the number of the desired automaticsubscriber or if the operator at the automatic exchange is desired, inaccordance with the number of a jack (not shown) terminating attheposition of the operator at the automatic exchange.

Insertion of plug 116 into ack 115 energizes relay 109 therebyestablishing a bridge from the lower trunk conductor, including coil106, winding of polarized relay 120, front contact and left-handarmature of relay 109 to the upper trunk conductor. Relay 120 thenoperates by current flowing over the conductors 100 and 102 from theswitches at the automatic exchange, and in closing its contactscompletes the circuit for relay 112 whereupon relay 125 is actuated andsignal 126 is extinguished. Insertion of plug 135 into jack 136 causesrelay 105 to operate, thereby connecting the impulse sender to the trunkconductors 100 and 102. hen relay 105 operates the continuity of thetrunk conductors is interrupted and relay 120 deenergizes. After theimpulses have been sent plug 135 is removed from jack 136, thecontinuity of the trunk conductors is restored, and relay 120 againenergizes.

Withdrawal of plug 116 from jack 115,

upon completion of conversatioi'i restores all relays at the manualexchange and the relays and busy signal at the automatic exchange tonormal.

Vhat is claimed is:

1. in a telcphone exchange system, a calling line, an operatorsposition, a two-conductor trunk circuit, a signaling device associatedwith said trunk circuit at said operators position, means. including aselector switch for extending said calling line over said trunk circuitto said operators position, a source of ringing current, andelectromagnetic means operating independently of said signaling deviceto cause the momentary connection of said source of ringing current tosaid trunk to actuate said signaling device upon seizure of the trunk bythe selector switch, and a locking circuit for said signaling devicecompleted upon actuation.

2. In a telephone exchange system, a trunk circuit, a signaling deviceconnected thereto, selector switch in which said trunk circuitterminates, means for setting said'selector switch on said trunkcircuit, a source of ringing current for actuating said signaling,device, a relay controlling the application of said ringing current tosaid trunk circuit, and means operating independently of said signalingdevice for causing a momentary energization of said relay upon theseizure of the trunk by the selector.

3. In a telephone system, a calling line, a

plurality of trunk circuits, a signaling device associated with eachtrunk circuit, means including a selector switch for connecting saidcalling line with an idle trunk circuit, a source of ringing current, arelay therefor, and means acting independently of said signaling deviceand upon the seizure of said trunk circuitfor establishin a transientcir til cuit in which said relay energizes to connect said ringingcurrent to said trunk and cause said signaling device to be actuated.

4. In a telephone exchange system, a first ofiice, a second otiice, aplurality oitrunk lines extending between said otiices, automaticswitching apparatus including selector switches at said first oliice forextending connections over said trunk, a signaling device associatedwith each trunk at the second oiiice, means including a line relay and aslow-to-release relay associated with the selector switch, forautomatically selecting an idle trunk, and means controlled by saidslow-to-release relay for actuating the signaling device of: theselected trunk.

5. In a telephone exchange system, a first office, a second cities, aplurality of trunk lines extending between said oiiices, automaticswitching apparatus including selector switches at said first oiiice forextending connections over said trunk, a signaling device associatedwith each trunk at the second oflice, means, including a line relay anda slow-to-release relay associated with the selector switch, forautomatically selecting an idle trunk, means controlled by saidslowto-release relay for actuating the signaling device of the selectedtrunk, and a locking circuit for said signaling device completed uponactuation.

6. .[n a telephone exchange system, a calling line, a trunk circuit, asignaling device associated with the trunk circuit, means in cluding aselector switch for extending the calling line to the trunk circuit, arelay associated with the trunk circuit adapted upon ene-rgization toproject a source of ringing current over the trunk to actuate thesignaling device, and means associated with the selector switch forcausing automatically the successive energization and deenergization ofthe relay.

7. In a telephone exchange system, a first and a second oiiice,subscribers lines terminating at each of'tice, a two-way trunk cir cuitextending between said oflices, means including automatic switchingapparatus for establishing a connection between the first and secondoffices, an operators position at the first oiiice, a signal at theoperators position at the first office for indicating when said trunk isbusy, a jack at the operators position at the first oiiice, an inductiveand a metallic path extending from the jack to the trunk circuit, meansfor enabling the operator to converse with the parties connected to saidtrunk over said inductive path, and means for enabling the operator toestablish a connection over said metallic path to the second oiiice whenthe trunk is idle.

8. In a telephone exchange system, a calling line, an operatorsposition, a two-way two-conductor trunk circuit, means includingautomatic switches for interconnecting the calling line and operatorsposition over the trunk circuit, a second operators position, means forpermitting the operator at the second position to supervise theconnection without interfering therewith, and 'T'-* means forinterconnecting the first mentioned and the second operators positionover the trunk circuit when it is idle.

9. In a telephone exchange system, a calling line, an operatorsposition, a two-way two-conductor trunk circuit, means includingautomatic switches for interconnecting the calling line and theoperators position over the trunk circuit, a second opcrators positionmeans for permitting the operator at the second position to supervisethe connection without interfering therewith, means for interconnectingthe first mentioned and the second operators position over the trunkcircuit when it is idle, and supervisory signals at each, operatorsposition for indicating disconnection.

10. In a telephone exchange system an automatic subscribers station, anoperators position, a two-way trunk circuit, means including automaticswitches for interconnecting the station and the operators position, asecond operators position, a jack thereat, an inductive and a metallicpath extending therefrom to the trunk circuit means for enabling theoperator at the second position to overhear the conversation of, andconverse with, the parties of an established connection over theinductive path without disturbing the connection, and means forcompleting a connection from the second operators position to the firstmentioned operators position over the metallic path when the trunk isidle.

11. In a telephone exchange system, an automatic subscribers station, anoperators position, a two-way trunk circuit, means including automaticswitches for interconnecting the station and the operators position, asecond operators position, a jack thereat, an inductive and a metallicpath extending therefrom to the trunk circuit, means for enabling theoperator at the second position to overhear over the inductive path theconversation of, and converse with, the parties of an establishedconnection without disturbing the connection, means for completing aconnection from the second operaitors position to the first mentionedoperators position over the metallic path when the trunk is idle, andmeans for rendering the trunk busy when in use by either the subscriber,the first mentioned or the second mentioned operator.

12. In a telephone exchange system, a calling line, an operatorsposition, a trunk line, means including automatic switches forestablishing a connection between the calling line and the operatorsposition, a second operators position, a jack thereat, two

paths over which said jack has access to the trunk circuit, one of thepaths being inductive and normally connected to the trunk and the otherbeing metallic and normally disconnected from the trunk, a cord circuitat the second operators position, means responsive to the connection ofthe cord circuit with the jack for preventing interference withsignaling over the trunk when the trunk is busy, and for enabling theoperator at the second position to listen in and converse with theparties to the connection, and means responsive tothe connection of thecord circuit with the trunk tor enabling the operator at the secondposition to establish a connection to the first mentioned position whenthe trunk is idle.

13. In a telephone exchange system, a railing line, an operatorsposition, means including automatic switches and a trunk circuit forinterconnecting the same, a second operators position, an operatorstelephone set thereat, means for connecting the operators telephone setto the trunk circuit, during the existence of a connection thereover,for listening and talking purposes, means for preventing such connectionfrom interfering with talking or signaling over the trunk, and means forcompleting a connection from the second operators position to the firstoperators position upon disconnection between the calling line and theoperators position.

14. In a telephone system, a calling line, a trunk circuit, a signalingdevice associated with the trunk circuit, means including a selectorswitch for extending the calling line to the trunk circuit, a source ofsignaling current, and means including a slow-to-release relayassociated with the selector switch and operable upon the seizure ofsaid trunk by said selector switch for causing the momentary applicationof said ringing current to said trunk to operate said signaling device.

15, In a telephone system, a calling line,

an operators position, a signaling device at said position, a trunkcircuit, means including a selector switch for interconnecting saidcalling line and said operators po sition by way of said trunk circuit,a source of signaling current, means including a slow-to-release relayassociated with the selector switch and operable upon the seizure ofsaid trunk circuit by said Selector switch for momentarily applying saidringing current to said trunk circuit to energize said signaling device,and means at said operators position for controlling the restoration ofsaid signaling device.

16. In a telephone system, a calling line, a trunk circuit, a signalingdevice associated with the trunk circuit, means including a selectorswitch for extending the calling line to the trunk circuit, a source ofsignaling current, means including a slow-to-release relay associatedwith the selector switch and operable upon the seizure of said trunk bysaid selector switch for causing the momentary application of saidringing current to said trunk to operate said signaling device, and alocking circuit for said signaling device completed upon actuation.

17, In a telephone system, a calling line, an operators position, asignaling device at said position, a trunk circuit, means ineluding aselector switch for inter-connecting said calling line and saidoperators position by way of said trunk circuit, a source of signalingcurrent, a slow-to-release relay associated with the selector switch andoperable upon the seizure of said trunk circuit by said selector switchfor applying said ringing current to said trunk circuit to energize saidsignaling device, a locking circuit for said signaling device completedupon actuation, and means controlled at said operators position forinterrupting said locking circuit In witness whereof, I hereuntosubscribe my name this 27th day of February A. D.,

RAY L. STOKELY.

